Radio service system



INVENTOR ATTONEY u 'Patented June 12A, 1945 I l RADIO SERVICE SYSTEM Richard A. mueriy, Baldwin, N. y., assigner' to Press Wireless, Inc., Chicago, Ill., a-corporation of Delaware Application september 1s, 1943, serial Nascar-11 4 Claims. (Cl. 250-8) possible at the This invention relates to radio transmitters and more' particularly to arrangements "-fwhereby van l existing radio transmitter operating at an as' receiver to demodulate the respective carrier shifts into mutually independent signed frequency may simultaneously be used to transmit more than two separate messages.

The invention is in the nature of an improvement on the kind of system disclosed in application Serial No. 498,278, flled August 12, 1943.

A principal object of the invention'relates to a radio transmitter system wherein the existing transmitter can be used to transmit two'or more intelligence signals by the carrier shift method.

A feature of the invention relates to a radio' transmitter having means to frequency shift the radio-frequency car'rier' over a number of discrete bands.

A further feature relates to the novel organization, arrangement and relative interconnection of parts which cooperate to produce a more efficient and iiexible service radio transmitter.

Other features and advantages not specifically enumerated will be apparent after a consideration 'of the following detailed descriptions and the appended claims.

Inasmuch as the invention relates to improved methods of plural message transmission on existing transmitters; only those parts of a radio transmission system will be schematically illus.

trated as are required for an understanding of o the inventive concept. Accordingly, in the drawing, there is shown in block diagram form a radio transmitter and receiver system embodying features of the invention. There is disclosed in application Serial No. 498,278, led Augilst 12, 1943,

a radio transmitter which is provided withspecial means for effecting' a -carrier shift to represent y two separate signals e. g., mark and space sents any well-known kind of telegraph keyingV signal-bearing channels. This latter is accom- -plished by -a specially designed radio receiver preferably, although not necessarily, of the superheterodyne type. I Y -v Referring to the drawing, the numeral I repredevice e. g., a tape or keyboard telegraph transmitter machine for producing mark and space signals. Associated with machine I is an oscillater 2 whose frequency can be shifted over a predeterminedgselected band under control of Ama- Y 8 radiates two discrete frequencieathe 'rst controlled by device l, and the second controlled by (in the case of telegraphy), and black and white (in the case of facsimile). At the' same time the shifted carrier is modulated in amplitude to transmit voice or similar' signals. Therefore, with the prior system two separate. kinds of intelligence signals can be simultaneously ltrans-A mitted, one by means of carrier shift, th other by amplitude modulation. In accordan e with the present invention the transmitter is p ovided withtwo or more carrier shift oscillators eachof whichv is independently variable in accordance with respective mark and space, or black and white signals. -By a special choice of the limits for eachof these carrier shift oscillators, itis possible to use each oscillator as a, separate but simultaneous control of the radio-frequency car- ,difference between the two will be 2 kc.

chine l. For example, oscillator2 may be shiftable between 156385 and 15639.0 kc., it being as" sumed that the, existing radio transmitter Soperates on an assigned frequency of 15640 kc. For

a detailed description of onepreferred manner of shifting the frequency of oscillator 2 between the desired limits, reference may be had to application Serial No. 498,278, filed `August 12, 1943.

A second shiftabie frequency oscillator 4 iscontrolled for vexample by a facsimile machine 5 whereby the black and white signals from machine 5, shift the frequency of oscillator 4 between predetermined limits, e. g., 15641.() and 156415 kc. At any given instant therefore, there are applied to the radio-frequency exciter stage A of the radio transmitter 3 two of the four sepa-Y rate frequencies. It will be understoodthat the amplifiers of transmitter 3 are designed to amplify uniformly the band between 156385 and 156415 kc. At any given instant therefore-the antenna device '5. If for example at any given instant, antenna 8 is radiating .on the upper frequency of 15639.@ kc. from oscillator 2 and also on the lower frequency limit 'of 15641.0 kc.- from device the Conversely, if antenna@ is radiating at the lower frequency 156385 kc.: from oscillator 2A and also the' upper frequency 156415 kc. from oscillator d,

the difference will be 3 kc.

At the receiving terminal or terminals, are located two radio receivers each tuned to itskrespective band Icorresponding to the frequency shift limits of oscillators 2 and 4. Preferably, however, -the receiving system is of thel superheterodyne type having a radio-frequency Aamplifier section 9 with its local oscillator I0; a rst detector Il which feeds two separate branched I. F. circuits rier shift without mutual interference, 'ande vit is 55 I2, i3, for converting the received radio-frequency signals into four respective I. F. signals for 463.5

kc., 464 kc., 46c-kc., and 466.5 Ykc. Each-1 F.

` l1 at 467.5 kc.

branch is provided with a second detector Il, I 5, each of which has a separate beat oscillator I8, l1. These beat oscillators operate on opposite sides of the mean I. F. of 465 kc.r For example, oscillator I6 operates at 462.5 kc., and oscillator Consequently, each of the I. F. signals can be demodulated independently. Since, as above described, the lowest best note resulting from the combinations of both radiated and received carriers is 2000 C. P. S., th'e beat oscillator frequencies are chosen sol that the receiver outputs from both branches in the audio-frequency spectrum lie below 2000 C. P. S. Thus, with the mentioned I. F. of 465 kc., one branch will produce in the receiver an I. F. lying between 463.5 kc. and 464 kc. Consequently, in conjunction with the beat frequency of 462.5 kc., the output 'of the first branch will lie between 1000 and 1500 C. P. S. Likewise, the beat frequency of 467.5 irc.,l in the second branch causes the audio-frequency output of that branch to lie between 1000 and 1500 C. P. S. Preferably, the audio-frequency output of each branch is passed through a respective band-pass filter I8,` I9, each having a band pass of iooo to 1500 c. P. s.y The altered audiofrequency output in each branch can then be used to control suitable respective telegraph and facsimile reproducers 20, 2|, in known manner.

While in the foregoing, it has been stated that the shifts of oscillators 2 and 4 are respectively L 500 C, P. S., that represents the preferred upper limit of' frequency shift. If desired, any smaller amount of shifts may be employed. Furthermore, while a system is employed using two separate carrier oscillators, it will be ,understood that a greater number may be employed. Thus each carrier shift oscillator may be shifted a maximum of 100 C. P. S. For example four separate oscillatorsk may be employed, one variable between 156385 kc. and 15638.6; another between 156383 and `156383 kc. :vanother between 15641.1,kc. and 15641.2 kc.; and a fourth between 15641.4 kc. and 156415 kc. Each of these separate oscillators will then be controlled as to its shifted frequencies in accordance with a separate message transmitter. At'Nthe receiver the respective shifted carriers are demodulated to derive the respective signals in each of four channels similar to those described in connection with channek I and 2.

Various changes and modifications may be made in the disclosed .embodiment |without departing from the spirit and scope of the invention.

What is claimed is: v 1. The method of operating "an existing radio@ `transmitter to increase its service usefulness,

. control of one kind of signal the frequency in one channel between predetermined frequency limits, shifting under control of a different kind of signal the frequency in the other channel between predetermined frequency limits, the actual frequency difference between the two channels being in the audio frequency range and whose meanjrequency is substantially the same as the normal assigned service frequency of the radio transmitter.

2. The method of operating an existing radio translnitter to increase its service usefulness,

. exciting -frequency from one limit toanother limitcorresponding to other signal conditions e. g. black and white, one of said frequency shifts being below the normal assigned-service frequency of the transmitter.

3. I'he method of operating an existing radio transmitter to increase its service usefulness, which comprises generating a first pair of audio frequency signals whose frequency difference is Fa, generating a second pair of audio frequency signals whose frequency difference is also Fa, shifting the frequency of a first radio oscillator under control of said first pair of signals and between frequency limits FI and F2 where FZ-Fi equals Fa, shifting the frequency of a second radio oscillator under control of said second pair of signals and between frequency limits F3 and F4 whereFL-F3 equals Fa, and simultaneously applying both shiftedfrequency oscillator outputs to a radio transmitter whose normal assigned service frequency is the mean between Fi and 4. In a radio system, a plurality of separate radio frequency oscillation sources a radio transmitter having an assigned normal service frequency `F, means to. simultaneously excite the transmitter with radio frequency oscillations of different frequency-ranges originating from said separate sources, means to'shift the frequency of l one source under control vof a rst signal, means to shiftthe frequency of the otherv source under control of another signal, the mean frequency of said shifted frequencies being approximately the said normal service frequency, and a common an- 5 5 tenna upon which both shifted Ifrequencies are impressed.

' RICHARD A. HILFER'I'Y. 

